The Reliability Optimization Of Bridge Crane Girder Based On Subset Simulation Method

Main girders, the most important part of the bridge, are the main bearing components of the machine. Once metal structure collapses, it will cause great property losses, so high reliability, namely, low failure probability, must be kept.So far, the design method of the bridge crane is still in the stage of allowable stress method or limit state design method. Monte Carlo method remains the main research method of all the probabilistic reliability calculation methods of bridge crane main girders. Although allowable stress method is simple to use, it is unable to gain a quantitative description of the reliability. Monte Carlo can solve the problems that allowable stress method encountered, but Monte Carlo requires a great number of samples in the calculation and it has a very low efficiency when calculating the small failure probabilities of bridge crane main girders. To solve the above problems, Subset Simulation method is introduced in this paper for the reliability analysis of the bridge crane girders. In this method,target failure events are expressed by a series of intermediate failure events and samples to simulate intermediate failure probabilities can be generated efficiently by Markov Chain Monte Carlo algorithm. The program to calculate the small failure probability is completed based on Matlab in this article and the feasibility and effectiveness of Subset Simulation are verified by practical engineering cases.Metal structure occupies at least 60% of the entire weight of bridge crane,metal structure design method based on the allowable stress method is old-fashioned, this leads to the big size and great weight of equipment and great costs of production, transportation and installation. So, the particle swarm algorithm is introduced in the metal structure design of bridge crane girder. On the bases of constraint conditions such as strength, stiffness and stability of the main girder, the reliability of the main girders is added extraordinarily, and the box girder cross section area of the bridge crane is regarded as the target function, then a mathematical reliability optimization design model of main girder is established. A reliability optimization design software of bridge cranebox girder is completed in the paper based on Microsoft VC++ 6.0 development platform. And the completed software is used in the reliability optimization of a certain bridge crane girder. The optimization result shows that, under the required design requirements, main girder cross section area is reduced 6.81%,this illustrates that the application of this software can reduce the weight and production costs of main girder and improve the economic benefit.